In some applications, a plurality of signals have to be sampled. Sampling in this respect relates to generating output values in regular or irregular intervals based on an input signal. For example, an analog signal may be digitized by an analog-to-digital converter (ADC) to output digital values (also referred to as samples) at a sampling rate. Also, instead of using an ADC an input signal may be compared to a threshold using a comparator, which results in one of two values (one indicating that the signal value exceeds the threshold and the other indicating that the signal value is below the threshold), thus essentially corresponding to a one-bit ADC.
One application where such a multi-channel sampling may be implemented is a monitoring of a plurality of different supply voltages in a device, e.g. a semiconductor device. For such a monitoring, each of the voltages may e.g. be compared to one or more respective thresholds, and when the respective voltage falls below a respective threshold, this may indicate an undervoltage, or, when the respective voltage is above a respective other threshold, this may indicate an overvoltage, where correct operation of the device may not be guaranteed. For example, such monitoring may be of particular importance in safety critical applications, e.g. automotive applications.
A conventional approach to monitoring a plurality of supply voltages is to provide one or more respective comparators for each of the supply voltages, each comparator having a respective threshold voltage. To test the device in a production test, a slow high-resolution linear ramp on the respective voltage rails for the supply voltages is used to determine a switching threshold hysteresis for each of the comparators. In some situations such comparators may not be accessible from outside the device, which requires additional effort as a unique special path for testing purposes may have to be provided.
Providing a plurality of comparators requires a comparatively large amount of circuit area which increases with the number of comparators required. Furthermore, in safety critical functions a second comparator may have to be added for redundancy for each supply voltage, leading to additional area requirements. Also, if testing circuitry is required, this may add to the total area.
One straightforward way to remedy this would be to multiplex all the channels into a single comparator, and also to multiplex corresponding thresholds to the comparator e.g. in a round robin fashion. However, this leads to a plurality of uniformly sampled voltages (voltages serving as an example for input signals). As in any uniformly sampled system the sampling theorem requires that the input signals must be bandlimited to half of the applicable sampling frequency (i.e. to the Nyquist frequency) to prevent aliasing, where essentially higher frequency components are “mirrored” to a baseband.
To prevent aliasing, anti-aliasing filters could be provided for each of the input signals (channels). However, providing such anti-aliasing filters increases the required chip area again. In particular, in case of high-voltage signals in the range of many tens of volts, the anti-aliasing filter needs to be implemented using corresponding high-voltage components. Also, in case an analog-to digital converter is used as a sampling device, the anti-aliasing filter would need to be an active filter so as not to increase the settling or sampling time of the analog-to-digital converter. Such active filters in many cases would not be smaller than a comparator itself, and therefore the total chip area required may even increase.
Instead of comparators as sampling devices also analog-to-digital converters may be used. In some cases, a plurality of comparators having different thresholds could be replaced by a single analog-to-digital converter, e.g. a SAR (Successive Approximation Register) analog-to-digital converter.
Therefore, it is an objective to provide devices and methods allowing multi-channel sampling, i.e. sampling of a plurality of input signals like input voltages, while requiring less chip area than some conventional solutions.